AQA 8525 · Section 3.4 · 3.4.4a

Operating System
Functions

Process Management · Memory Management · File Management · Security

CSZoneAQA GCSE Computer Science 8525

Six Key OS Functions

What the OS Does

Process Management — allocates CPU time to running programs; handles multitasking using scheduling

Memory Management — allocates RAM to processes; uses virtual memory when RAM is full

File Management — organises files in a directory structure; handles read/write/delete operations

Device Management — controls peripherals via device drivers (printers, keyboards, mice)

Security — user authentication, access control, preventing unauthorised access

User Interface — provides a way for users to interact with the computer (GUI or CLI)

Process Management

Multitasking and Scheduling

Modern computers appear to run many programs simultaneously. In reality, the CPU rapidly switches between processes. The OS uses scheduling algorithms to decide which process gets CPU time and for how long.

Multi-programming — multiple programs loaded in RAM, CPU switches between them

Context switching is so fast it feels instant to the user

OS keeps track of process state (running, waiting, blocked)

Memory Management

Allocating RAM and Virtual Memory

RAM ALLOCATION

The OS divides RAM between running processes. Each gets its own protected area to prevent interference.

VIRTUAL MEMORY

When RAM is full, the OS uses part of the hard disk as overflow memory. Slower than RAM but prevents crashes.

Trade-off:More RAM = less virtual memory needed = faster performance. Disk-based virtual memory is ~100× slower than RAM.

Exam Practice

Have a go at this question

AQA-style question

Describe two functions of an operating system.

4 marks

Process management: the OS allocates CPU time to different running programs using scheduling algorithms, enabling multitasking [1] so multiple programs appear to run simultaneously [1].

Memory management: the OS allocates sections of RAM to each running process [1] and uses virtual memory (hard disk space) when RAM is full [1].

Key Takeaways

What to Remember

OS manages: processes, memory, files, devices, security, UI

Multitasking: CPU rapidly switches between processes — scheduling decides priority

Virtual memory: uses disk as overflow when RAM is full — slower but prevents crashes

Device drivers let the OS communicate with specific hardware peripherals